1. Field of the Invention
This invention relates to a composite optical device and its manufacturing method suitable for a composite optical device in which an optical element such as prism, for example, is bonded to a support body with an adhesive.
2. Related Art
Among conventional composite optical devices of this type, there is a device called laser coupler. Such a conventional laser coupler used as an optical pickup of a CD player, for example, is shown in FIGS. 1 and 2. FIG. 1 is a perspective view of the laser coupler, and FIG. 2 is a longitudinal cross-sectional view of the same laser coupler. As shown in FIGS. 1 and 2, the laser coupler comprises a microprism 102 made of optical glass and a LOP (laser on photodiode) chip consisting of a photodiode 103 and a semiconductor laser 104 supported thereon, which are mounted on a photodiode IC 101 in a close relationship. The photodiode IC 101 includes a pair of photodiodes PD1 and PD2 for detecting an optical signal, a current-to-voltage (I-V) converting amplifier and an arithmetic processing unit (not shown) which all are incorporated into IC. The photodiode 103 is configured to monitor light output from a rear end surface of the semiconductor laser 104 and to control light output from a front end surface of the semiconductor laser 104.
As shown in FIG. 2, the microprism 102 has a half mirror 105 on its slanted surface 102a, a total reflection film 106 on its top surface 102b, an antireflection film 107 on its bottom surface 102c, a mirror plane comprising its end surface 102d facing to the LOP chip, and a light absorbing film 108 on its end surface 102e opposite from the LOP chip. The antireflection film 107 on the bottom surface 102c of the microprism 102 is covered by a SiO.sub.2 film 109. The microprism 102 is mounted on the photodiode IC 101 by an adhesive 110 applied to the SiO.sub.2 film 109. The SiO.sub.2 film 9 is used to reinforce the adhesive force of the adhesive 110 for holding the microprism 102 on the photodiode IC 101. Used as the half mirror 105 is, for example, an amorphous Si film which is made by vacuum evaporation. Used as the total reflection film 106 is, for example, a dielectric multi-layered film including 20 layers of SiO.sub.2 and 20 layers of TiO.sub.2 which are stacked alternately. Used as the antireflection film 107 is, for example, a CeF.sub.3 film. Used as the light absorbing film 108 is, for example, a Cr/CrO-based multi-layered film. In certain cases, the microprism 102 has a half mirror on one half of the antireflection film 107 on the bottom surface 102c located nearer to the LOP chip.
The laser coupler having the above construction is contained in a flat package 111 made of, for example ceramics, and sealed by a window cap, as shown in FIG. 3.
As shown in FIGS. 1 and 2, in the laser coupler described above, a laser beam L exerted from the front end surface of the semiconductor laser 104 is reflected by the half mirror 105 on the slanted surface 102a of the microprism 102, and runs toward a disc (not shown) for reading a signal from the laser beam L. The laser beam L reflected by the disc passes through the half mirror 105 and enters in the microprism 102 from its slanted surface 102a. One half of the beam enters into the photodiode PD1, and the other half beam enters into the photodiode PD2 after sequentially reflected by the surface of the photodiode PD1 and the top surface 102b of the microprism 102. When the laser beam L focalizes on a recording plane of the disc, spot sizes on front and rear photodiodes PD1 and PD2 are equal; however, if the focalization is out of the recording plane, then the spot sizes on the photodiodes PD1 and PD2 differ from each other. Then, if the deviation of focalization appears as a difference between output signals from the photodiodes PD1 and PD2, a focus error signal can be detected. The point where the focus error signal is zero corresponds to the point in which the focalized position lies on the recording plane of the disc, that is, the just focus point. By a feedback control of a focus servo system such that the focus error signal becomes zero, the just-focus state can be maintained, and the disc can be reproduced in a good condition.
Conventional laser coupler, as described above, are manufactured in the following method.
As shown in FIG. 4, a photodiode IC wafer 111 is first prepared through a given wafer process. Reference numeral 111a denotes a chip region corresponding to a single photodiode IC.
Next, as shown in FIG. 5, LOP chips are mounted on respective chip regions 111a of the photodiode IC wafer 111 by silver paste (not shown) and then subjected to an appropriate curing treatment.
In the next step, as shown in FIG. 6, bar-shaped microprisms 102 each extending over a plurality of chip regions 111a, e.g. ten chip regions, on the photodiode IC wafer 111 are provisionally fixed by using a silicone-resin-based adhesive (not shown) which cures when exposed to ultraviolet rays. After that, a curing treatment is effected, that is, the adhesive is set by irradiation of ultraviolet rays.
In the next step, the back surface of the photodiode IC wafer 111 is bonded to an extensible sheet (not shown). Then, as shown in FIG. 7, each bar-shaped microprism 102 is half-cut by using an appropriate dicer (dicing unit, not shown).
After that, each bar-shaped microprism 102, adhesive 110 and photodiode IC wafer 111 are full-cut with the dicer to finally obtain separate chips, i.e. individual photodiode ICs, as shown in FIG. 8.
Then the extensible sheet is extended to isolate the respective chips from each other, and each chip is picked up and packaged as shown in FIG. 3.
In the conventional laser coupler manufacturing method described above, when the photodiode IC wafer 111 is full-cut by the dicer, the bar-shaped microprism 102, adhesive 110 and photodiode IC wafer 111 are cut sequentially. In this cutting process, swarf is produced and adheres on the surfaces of the microprism 102 and the photodiode IC 101. Since the slanted surface 102a and the top surface 102b of the microprism 102 behave as the plane of incidence of light and the light reflective plane, contamination of these surfaces adversely affect incidence and reflection of the laser beam L. To prevent this, the conventional method washes away the swarf by spraying water to the cut portion and the blade of the dicer during the cutting, and removes dust by spraying water and blowing dry air after the cutting.
Silicone resin, however, which is used as the adhesive 110, has a stickiness, its swarf adheres onto the surfaces of the microprism 102 and other element and remains even after the washing mentioned above.
This problem is not limited to laser couplers but applies to composite optical devices, in general, which are made by bonding a bar-shaped optical element on a support body by means of an adhesive, especially a resin-based adhesive, and subsequently cutting the semi-product into individual devices with an appropriate dicer or a like apparatus. Therefore, there is a strong demand for solution of the problem.